in reply to Re^4: Accessing lexicals in other scopes dynamically by name
in thread Accessing lexicals in other scopes dynamically by name

I think it's an optimisation. Capturing all lexicals would cause a closure to take longer to create, use more memory and prevent another optimisation that reuses lexicals from previous calls to the function.
  • Comment on Re^5: Accessing lexicals in other scopes dynamically by name

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Re^6: Accessing lexicals in other scopes dynamically by name
by morgon (Priest) on Jul 30, 2010 at 20:36 UTC
    Hmm.

    I have never really looked at the Perl-internals, but I can vagly remember having seen an implementation of Scheme in Scheme.

    If I remember correctly there was a data-structure containing all the variable-bindings for any lexical scope and every closure would simply keep a reference to this.

    So in this approach there is not a "capturing of all lexicals" but simply remembering one data-structure regardless of how many variables were defined it.

    Perl evidently does this differently and I even think that the inaccessabilty of certain lexial variables of which Perl could not see that the are going to be used in a closure is a weakness.

    I will try this in Rakudo.

[reply]

      So in this approach there is not a "capturing of all lexicals" but simply remembering one data-structure regardless of how many variables were defined it.

      You forgot the bit about placing them in the data structure to being with.

[reply]
        You forgot the bit about placing them in the data structure to being with.
        I made it not clear I think.

        This structure is initialized when a new lexial scope is encountered (pointing back to the enclosing environment) and new variable bindings are added whenever a new lexial variable is defined.

        It exists whether or nor a closure is created.

        All closures within this context then simply remember a reference to this structure and use it to look up variables.

        But Perl evidently does it differently it does not really matter..

[reply]

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